#include <mruby.h>

#ifndef MRB_NO_FLOAT

#include <string.h>
#include <math.h>
#include <stdint.h>

// Powers of 10 lookup table for better performance and accuracy
static const double pow10_positive[] = {
  1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9,
  1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19,
  1e20, 1e21, 1e22, 1e23, 1e24, 1e25, 1e26, 1e27, 1e28, 1e29,
  1e30, 1e31, 1e32, 1e33, 1e34, 1e35, 1e36, 1e37, 1e38, 1e39,
  1e40, 1e41, 1e42, 1e43, 1e44, 1e45, 1e46, 1e47, 1e48, 1e49,
  1e50, 1e51, 1e52, 1e53, 1e54, 1e55, 1e56, 1e57, 1e58, 1e59,
  1e60, 1e61, 1e62, 1e63, 1e64, 1e65, 1e66, 1e67, 1e68, 1e69,
  1e70, 1e71, 1e72, 1e73, 1e74, 1e75, 1e76, 1e77, 1e78, 1e79,
  1e80, 1e81, 1e82, 1e83, 1e84, 1e85, 1e86, 1e87, 1e88, 1e89,
  1e90, 1e91, 1e92, 1e93, 1e94, 1e95, 1e96, 1e97, 1e98, 1e99,
  1e100, 1e101, 1e102, 1e103, 1e104, 1e105, 1e106, 1e107, 1e108, 1e109,
  1e110, 1e111, 1e112, 1e113, 1e114, 1e115, 1e116, 1e117, 1e118, 1e119,
  1e120, 1e121, 1e122, 1e123, 1e124, 1e125, 1e126, 1e127, 1e128, 1e129,
  1e130, 1e131, 1e132, 1e133, 1e134, 1e135, 1e136, 1e137, 1e138, 1e139,
  1e140, 1e141, 1e142, 1e143, 1e144, 1e145, 1e146, 1e147, 1e148, 1e149,
  1e150, 1e151, 1e152, 1e153, 1e154, 1e155, 1e156, 1e157, 1e158, 1e159,
  1e160, 1e161, 1e162, 1e163, 1e164, 1e165, 1e166, 1e167, 1e168, 1e169,
  1e170, 1e171, 1e172, 1e173, 1e174, 1e175, 1e176, 1e177, 1e178, 1e179,
  1e180, 1e181, 1e182, 1e183, 1e184, 1e185, 1e186, 1e187, 1e188, 1e189,
  1e190, 1e191, 1e192, 1e193, 1e194, 1e195, 1e196, 1e197, 1e198, 1e199,
  1e200, 1e201, 1e202, 1e203, 1e204, 1e205, 1e206, 1e207, 1e208, 1e209,
  1e210, 1e211, 1e212, 1e213, 1e214, 1e215, 1e216, 1e217, 1e218, 1e219,
  1e220, 1e221, 1e222, 1e223, 1e224, 1e225, 1e226, 1e227, 1e228, 1e229,
  1e230, 1e231, 1e232, 1e233, 1e234, 1e235, 1e236, 1e237, 1e238, 1e239,
  1e240, 1e241, 1e242, 1e243, 1e244, 1e245, 1e246, 1e247, 1e248, 1e249,
  1e250, 1e251, 1e252, 1e253, 1e254, 1e255, 1e256, 1e257, 1e258, 1e259,
  1e260, 1e261, 1e262, 1e263, 1e264, 1e265, 1e266, 1e267, 1e268, 1e269,
  1e270, 1e271, 1e272, 1e273, 1e274, 1e275, 1e276, 1e277, 1e278, 1e279,
  1e280, 1e281, 1e282, 1e283, 1e284, 1e285, 1e286, 1e287, 1e288, 1e289,
  1e290, 1e291, 1e292, 1e293, 1e294, 1e295, 1e296, 1e297, 1e298, 1e299,
  1e300, 1e301, 1e302, 1e303, 1e304, 1e305, 1e306, 1e307, 1e308
};

static const double pow10_negative[] = {
  1e0, 1e-1, 1e-2, 1e-3, 1e-4, 1e-5, 1e-6, 1e-7, 1e-8, 1e-9,
  1e-10, 1e-11, 1e-12, 1e-13, 1e-14, 1e-15, 1e-16, 1e-17, 1e-18, 1e-19,
  1e-20, 1e-21, 1e-22, 1e-23, 1e-24, 1e-25, 1e-26, 1e-27, 1e-28, 1e-29,
  1e-30, 1e-31, 1e-32, 1e-33, 1e-34, 1e-35, 1e-36, 1e-37, 1e-38, 1e-39,
  1e-40, 1e-41, 1e-42, 1e-43, 1e-44, 1e-45, 1e-46, 1e-47, 1e-48, 1e-49,
  1e-50, 1e-51, 1e-52, 1e-53, 1e-54, 1e-55, 1e-56, 1e-57, 1e-58, 1e-59,
  1e-60, 1e-61, 1e-62, 1e-63, 1e-64, 1e-65, 1e-66, 1e-67, 1e-68, 1e-69,
  1e-70, 1e-71, 1e-72, 1e-73, 1e-74, 1e-75, 1e-76, 1e-77, 1e-78, 1e-79,
  1e-80, 1e-81, 1e-82, 1e-83, 1e-84, 1e-85, 1e-86, 1e-87, 1e-88, 1e-89,
  1e-90, 1e-91, 1e-92, 1e-93, 1e-94, 1e-95, 1e-96, 1e-97, 1e-98, 1e-99,
  1e-100, 1e-101, 1e-102, 1e-103, 1e-104, 1e-105, 1e-106, 1e-107, 1e-108, 1e-109,
  1e-110, 1e-111, 1e-112, 1e-113, 1e-114, 1e-115, 1e-116, 1e-117, 1e-118, 1e-119,
  1e-120, 1e-121, 1e-122, 1e-123, 1e-124, 1e-125, 1e-126, 1e-127, 1e-128, 1e-129,
  1e-130, 1e-131, 1e-132, 1e-133, 1e-134, 1e-135, 1e-136, 1e-137, 1e-138, 1e-139,
  1e-140, 1e-141, 1e-142, 1e-143, 1e-144, 1e-145, 1e-146, 1e-147, 1e-148, 1e-149,
  1e-150, 1e-151, 1e-152, 1e-153, 1e-154, 1e-155, 1e-156, 1e-157, 1e-158, 1e-159,
  1e-160, 1e-161, 1e-162, 1e-163, 1e-164, 1e-165, 1e-166, 1e-167, 1e-168, 1e-169,
  1e-170, 1e-171, 1e-172, 1e-173, 1e-174, 1e-175, 1e-176, 1e-177, 1e-178, 1e-179,
  1e-180, 1e-181, 1e-182, 1e-183, 1e-184, 1e-185, 1e-186, 1e-187, 1e-188, 1e-189,
  1e-190, 1e-191, 1e-192, 1e-193, 1e-194, 1e-195, 1e-196, 1e-197, 1e-198, 1e-199,
  1e-200, 1e-201, 1e-202, 1e-203, 1e-204, 1e-205, 1e-206, 1e-207, 1e-208, 1e-209,
  1e-210, 1e-211, 1e-212, 1e-213, 1e-214, 1e-215, 1e-216, 1e-217, 1e-218, 1e-219,
  1e-220, 1e-221, 1e-222, 1e-223, 1e-224, 1e-225, 1e-226, 1e-227, 1e-228, 1e-229,
  1e-230, 1e-231, 1e-232, 1e-233, 1e-234, 1e-235, 1e-236, 1e-237, 1e-238, 1e-239,
  1e-240, 1e-241, 1e-242, 1e-243, 1e-244, 1e-245, 1e-246, 1e-247, 1e-248, 1e-249,
  1e-250, 1e-251, 1e-252, 1e-253, 1e-254, 1e-255, 1e-256, 1e-257, 1e-258, 1e-259,
  1e-260, 1e-261, 1e-262, 1e-263, 1e-264, 1e-265, 1e-266, 1e-267, 1e-268, 1e-269,
  1e-270, 1e-271, 1e-272, 1e-273, 1e-274, 1e-275, 1e-276, 1e-277, 1e-278, 1e-279,
  1e-280, 1e-281, 1e-282, 1e-283, 1e-284, 1e-285, 1e-286, 1e-287, 1e-288, 1e-289,
  1e-290, 1e-291, 1e-292, 1e-293, 1e-294, 1e-295, 1e-296, 1e-297, 1e-298, 1e-299,
  1e-300, 1e-301, 1e-302, 1e-303, 1e-304, 1e-305, 1e-306, 1e-307, 1e-308, 1e-309,
  1e-310, 1e-311, 1e-312, 1e-313, 1e-314, 1e-315, 1e-316, 1e-317, 1e-318, 1e-319,
  1e-320, 1e-321, 1e-322, 1e-323
};

#define POW10_POSITIVE_SIZE (sizeof(pow10_positive) / sizeof(pow10_positive[0]))
#define POW10_NEGATIVE_SIZE (sizeof(pow10_negative) / sizeof(pow10_negative[0]))

static double
mrb_pow10(int exp)
{
  if (exp >= 0) {
    if (exp < (int)POW10_POSITIVE_SIZE) {
      return pow10_positive[exp];
    }
    return HUGE_VAL;
  }
  else {
    exp = -exp;
    if (exp < (int)POW10_NEGATIVE_SIZE) {
      return pow10_negative[exp];
    }
    return 0.0;
  }
}

/*
** Parses a string representation of a floating-point number.
**
** @param str The input string to parse.
** @param endp A pointer to a char* that will be updated to point to the
**             character in str after the last character used in the
**             conversion. Can be NULL.
** @param fp A pointer to a double that will be set to the parsed
**           floating-point number.
** @return TRUE if a float is successfully parsed, FALSE otherwise.
*/
MRB_API mrb_bool
mrb_read_float(const char *str, char **endp, double *fp)
{
  const char *p = str;
  const char *a = p;
  uint64_t int_part = 0;
  uint64_t frac_part = 0;
  int frac_digits = 0;
  int sign = 1;
  int digits = 0;
  int overflow = 0;

  // Skip whitespace
  while (ISSPACE((unsigned char)*p)) p++;

  // Handle sign
  if (*p == '-') { sign = -1; p++; }
  else if (*p == '+') p++;

  // Parse integer part using integer arithmetic for better accuracy
  while (ISDIGIT(*p)) {
    if (int_part > (UINT64_MAX - 9) / 10) {
      overflow = 1;
      // Continue parsing to find the end
      while (ISDIGIT(*p)) p++;
      break;
    }
    int_part = int_part * 10 + (*p - '0');
    digits++;
    a = ++p;
  }

  // Parse fractional part
  if (*p == '.') {
    p++;
    while (ISDIGIT(*p) && frac_digits < 17) { // Limit precision to avoid overflow
      frac_part = frac_part * 10 + (*p - '0');
      frac_digits++;
      digits++;
      p++;
    }
    // Skip remaining fractional digits if any
    while (ISDIGIT(*p)) p++;
    a = p;
  }

  // If no digits were found, return FALSE
  if (digits == 0) {
    if (endp) *endp = (char*)str;
    *fp = 0.0;
    return FALSE;
  }

  double res;
  if (overflow) {
    // For overflow case, fall back to floating point parsing
    res = (double)int_part;
  }
  else {
    // Fast path: combine integer and fractional parts
    res = (double)int_part;
    if (frac_digits > 0) {
      res += (double)frac_part * mrb_pow10(-frac_digits);
    }
  }

  // Handle exponent
  if ((*p | 32) == 'e') {
    int e = 0;
    int exp_sign = 1;
    p++;
    if (*p == '-') { exp_sign = -1; p++; }
    else if (*p == '+') p++;

    // If no digits follow 'e', ignore the exponent part
    if (!ISDIGIT(*p)) goto done;

    while (ISDIGIT(*p)) {
      if (e < 10000) { // Prevent integer overflow
        e = e * 10 + (*p - '0');
      }
      p++;
    }
    e *= exp_sign;

    // Apply exponent directly - let mrb_pow10 handle overflow
    // Large exponents will return HUGE_VAL (infinity) or 0.0 as appropriate

    res *= mrb_pow10(e);
    a = p;
  }

  // Apply sign
  res *= sign;

  // Set endp
 done:
  if (endp) *endp = (char*)a;
  *fp = res;

  // strtod(3) stores ERANGE to errno for overflow/underflow
  // mruby does not require those checks
#if 0
  // Check for underflow after applying the exponent
  if (res != 0.0 && fabs(res) < DBL_MIN) {
    return FALSE;
  }

  // Check if the result is infinity or NaN
  if (isinf(res) || isnan(res)) {
    return FALSE;
  }
#endif
  return TRUE;
}

#endif
